1. Field of the Invention
The present invention relates to an optical fiber ribbon fusion-splicing device and, more particularly, to an improvement in the resolution of an image of fibers of an optical fiber ribbon.
2. Description of the Related Art
A method of fusion-splicing optical fiber ribbons is known which comprises, as shown in FIG. 1, steps performed prior to a fusion-splicing step, of placing exposed portions 12.sub.1 and 12.sub.2 of the fibers of a pair of optical fiber ribbons 10.sub.1 and 10.sub.2 on a pair of grooved supporting members 11.sub.1 and 11.sub.2, respectively, so that the exposed fibers 12.sub.1 and 12.sub.2 are arranged in the coaxial direction of the supporting members 11.sub.1 and 11.sub.2, of clamping the fiber ribbons 10.sub.1 and 10.sub.2 with a pair of clamps 13.sub.1 and 13.sub.2, respectively, of moving the clamps towards each other so that the joining ends of the fibers 12.sub.1 and 12.sub.2 close to each other, and of monitoring the alignment of the joining portions of the fibers. For monitoring the fiber alignment, a TV camera 16 is incorporated in the device to pick up via an optical system 26 including an objective lens 14 a light beam having passed through the fibers 12.sub.1 and 12.sub.2 to form images of the joining portions of the fibers. The images 12.sub.1 ' and 12.sub.2 ' are displayed on the screen 20 of a TV monitor 18. The joining portions of the fibers 12.sub.1 and 12.sub.2 are monitored to determine whether they are aligned or not. If misalignment exists, an alarm-sound is given or an alarm-sign is displayed on the screen. Then, the fiber ribbons 10.sub.1 and 10.sub.2 are removed from the clamps 13.sub.1 and 13.sub.2, and the above setting operation is repeated. When the misalignment is within a permissible range, the clamps 13.sub.1 and 13.sub.2 are further advanced toward each other to further advance the fibers 12.sub.1 and 12.sub.2 towards each other with their joining ends being pressed and fusion-spliced to each other by means of an arc generated by applying a high voltage across a pair of electrodes 22.sub.1 and 22.sub.2. A reflecting mirror 24 is provided behind the fibers 12.sub.1 and 12.sub.2.
The monitoring will be carried out to determine the fiber alignment before and after the fusion-splicing procedure.
In order that an image of the entire of the joining portions of the fibers is provided in a form of a single frame, the entire of the joining portions has to be fallen within a field of view of the TV camera 16 or an image sensor 17.
Meanwhile, the number of fibers of an optical fiber ribbon has been increased to enhance the packing density, and 12-fiber optical fiber ribbon is now introduced for practical use. Also in aligning such optical fiber ribbons having an increased number of fibers, the entire of the joining portions of the fibers should be picked up within the view field of a TV camera in order to provide an image of the entire of the joining portions of the fibers in a form of a single frame. In order to pick up the entire joining portions, in a prior art method, the power factor of the TV camera is lowered to expand the view field of the camera. As the result, the resolution of the image on the screen is decreased and the fiber misalignment will be detected with less accuracy.
In a prior art method, the joining portions of fibers of an optical fiber ribbon having less than 8-fibers can be displayed at high resolution on a monitor screen, and the alignment can be determined with an accuracy of less than 1.0 .mu.m, even when the power factor of the TV camera is reduced so that the entire joining portions can be exhibited within a view field of the TV camera.
However, when it is required that the entire joining portions of the fibers of 12-fiber optical fiber ribbon be taken into the view field, the power factor is greatly lowered, and the resolution of the fiber image displayed on the monitor screen will be decreased, thus resulting in less accurate monitoring.
In the prior art device, the TV camera 16 is set such that the horizontal direction (H-direction in FIGS. 1 and 2) of the image sensor 17 in which direction a horizontal scanning is carried out and the resolution of the image sensor is higher than that in the vertical direction (V-direction in FIGS. 1 and 2) in which a vertical scanning is carried out corresponds to or coincides with the coaxial direction (X-direction in FIGS. 1 and 2) of the grooved supporting members 11.sub.1 and 11.sub.2, so that, when fibers 12.sub.1 and 12.sub.2 of a pair of optical fiber ribbons 10.sub.1 and 10.sub.2 are set on the supporting members in the coaxial direction thereof, the horizontal direction of the image sensor corresponds to or coincides with the coaxial direction (X-direction in FIGS. 1 and 2) of the fibers of the optical fiber ribbons. In misalignment, the fibers 12.sub.1 and 12.sub.2 are displaced from each other in the direction (Y-direction in FIGS. 1 and 2) perpendicular to the coaxial direction (X-direction in FIGS. 1 and 2) of the fibers, and thus the displacement is seen in the vertical direction (V-direction) on the image sensor. In order to enhance the accuracy in detection of misalignment, we may increase the V-directional resolution of the image sensor, thereby to provide the image of the joining portions of the fibers with high resolution. However, in fact, even when the V-directional resolution of the image sensor is increased, the resolution of the image of fibers displayed on the TV screen cannot be enhanced, since video signals for TV image reproduction are designated in the standard specification, thus limiting the V-directional resolution of the TV monitor.
The problem associated with the prior art is that a the number of fibers of an optical fiber ribbon is increased, the resolution of the video image of the fibers displayed on a screen is decreased, thus lowering accuracy in detection of misalignment.